Friday, January 18, 2008

RWS 850 AirMagnum PCP Conversion - Part 1

by A.R. Tinkerer

My start in airguns came in about 2005 with the purchase of a Crosman 781AK kit. I was unfamiliar with airguns and three of its features clinched the sale. The 781 is a single pump, multi-shot, BB and pellet gun. I don't remember why the dual ammo attracted me, but it did. I intended to use it for pest control and since I didn't shoot much, I wanted to be able to take a quick follow-up shot. I figured the multi-shot and single pump features fit this bill. This was also a spur of the moment purchase.

Fortunately, about that time, I came across the Pyramyd Air blog. After doing some reading, I began to realize the 781 was not powerful enough for pest control. So began my search for the perfect airgun. The RWS 850 AirMagnum had recently been introduced and seemed to be a good choice. If the Benjamin Discovery had been available at the time, I would have bought it (even though it wasn't a repeater)! This post also wouldn't be here (and probably not this blog). Anyway, I ordered the .22 caliber AirMagnum and couldn't wait to use it after sighting it in. Soon I had a chance.

To make a long story shot, I shot a pest that we had problems with. However, it wasn't a quick kill, so I decided I needed more power. I had read that using air in a CO2 airgun would increase the power, so I began to research a conversion for my gun. Later I discovered that one problem was that I should have taken a head shot.

The First Conversion
I did quite a bit of research on the web to figure out how to convert to air. What I found is that paintball is a great resource! My requirements for the conversion were to keep it simple and use off the shelf parts, and most of these were available from paintball stores. But I had one problem. I couldn't find an adapter to convert the AirMagnum's Crosman AirSource connection to a paintball ASA.

Some Paintball Terms
ASA - Air Source Adapter, the adapter a paintball tank screws into
HPA - High Pressure Air; high pressure air is sometimes used instead of CO2 (carbon dioxide)
Marker - official term for a paintball "gun"
Remote - setup that connects the paintball tank to a paintball marker

One problem I had with finding an adapter was that I didn't know exactly what I was looking for. I started thinking about how I could cut off the threaded part of the AirSource bottle, drill it, thread it and other creative ideas. It all seemed like a lot of work to me!

Crosman AirSource cut open

Finally I ran across an AirSource to Paintball adapter from Cooper-T. That was the ticket! It was a Crosman AirSource to ASA adapter with a check valve. After buying the adapter, I also bought a relatively inexpensive HPA tank and remote. I had everything I needed!

Remote quick disconnect; Cooper-T adapter (red)

Remote with Cooper-T adapter

A note about Cooper-T
Unfortunately the man who ran Cooper-T passed away. The Cooper-T web site is still up, apparently to clear out inventory. There are some complaints on the web about long waits getting Cooper-T parts now, but that may be understandable given the circumstances. Other sources for AirSource to ASA adapters have become available recently. My condolences to Cooper-T's family.

Now that I had my conversion, I was anxious to try it. I found instructions for a DIY chronograph and set up my own. For my setup, my first paper was 5 feet from the gun and the second paper was 10 feet from the first paper (15 feet from the gun). I set the microphone recording volume to 50% (but NO microphone +20dB boost) and started recording.

The conversion of the .22 caliber 850 AirMagnum performed as follows with Nitrogen. I used Nitrogen for this test because the paintball store I filled at only filled with Nitrogen. JSB Exact Jumbos were used for the test and velocities ranged from 591fps up to 602fps with an average of 594fps (12.38 average foot pounds). That makes this setup about the same as CO2 on an 80 - 90 degree day. (The CO2 results for comparison came from comments on the Pyramyd Air blog.) It was 73 degrees Fahrenheit the day I tested.

Disappointing Results?
Was I disappointed with the results? Yes. I was hoping for better than CO2 performance, not just the same as CO2 at higher temperatures. The tank and remote setup is also kind of clumsy.

Things Learned
-Know what power level you need for hunting different size pests.
-Know where to aim to be humane when hunting. This may be different than where you would aim with a firearm.
-Quite a bit about paintball, high pressure air and air fittings.

What Now?
I have gone through a couple more versions of the conversion that I will describe in future posts. When I am done with my latest version, I will also post that. Following are a few projects/discussions I am planning for the future.
-Discussion on air power feasibility: problems and some solutions
-Discussion on possible uses of air power
-More installments on the RWS 850 AirMagnum conversion
-Air powered R/C plane
-DIY chronograph (using phototransistors)


DragonSlayer said...

Multi: Was looking for a simple Hi from BB., talk about a "plug",, You have rec. the ultimate respect! BB. once again goes above & beond! WOW!! Main post! Congrats. my friend!! Following your 850 conv. Closely. & will cont. Saw your ref. to R.C. planes,,Off subject I know, But I have 6!! Not air powered, (most are O.S. Max (World Engines) Nitro burners!) Have 4-6 chnl. Futaba,Century, (circus),& most recent JR.Radios! 6 planes from high wing "stick" trainers to Super KAOS&Miss Martha W/60 engines! KAOS has ret. landing gear & chnl. left for ? Bomb drop?? Have not flown any in last 2 years,since my addiction to airguns!! Could it be that your R.C. post about air power could refer to a co-2 powered Micro Light?? Ill go back & see! Co2 micro would be ok,, But HPA 12 gr. for Micro Lites would be AWSOME!! (rechargable of course!) Thanks Multi/Tink? Tim. P.S.,Happy for you my Friend!! Tim in S.C.

CyberSkin said...

22 multi shot
Sorry to hear that got minimal improvement in your efforts, but how else are we supposed to learn. Its people like you that we must rely on to mod our guns. Just don't get hurt or lose sight of other things and burn yourself out.

I guess that we got into the air gun hobby about the same time. I wish that I knew then what I do now.

My other hobby for some time has been over clocking computers. A good resource is Its a addiction that is rewarding. Check it out.

Anonymous said...

Of course you only got CO2 performance. HPA tanks are regulated to opperate at CO2 pressures (about 850 psi). If you want higher velocity, you have to modify the regulator to output higher pressures. You must be careful though, too high and you will ruin the gun and risk injury.

A.R. Tinkerer said...


Yah, was I surprised!

I currently own 3 planes. The Estes Sky Rangers "Jet" (really ducted fan), Air Hogs Aero Ace (biplane) and Mini Blue Max. I am currently building the Mini Blue Max so you've got me beat!

No comment on the air powered R/C plane. I have some ideas, but I haven't started experimenting yet.


A.R. Tinkerer said...


I was disappointed, but that isn't stopping me. I do a lot of research before trying something - I don't want to die or go through life disabled! Thanks for your concern.

I overclocked one computer I built years ago, but I stopped building my own computers. It gives me more time for other things.

I wish I knew what I know now when I started with airguns too!


A.R. Tinkerer said...


Note that it wasn't the same as CO2 performance at 73 degrees though! The nitrogen molecule is smaller than CO2 and flows easier. This is true of air too since it is mostly made up of nitrogen.

Stayed tuned for the next installment. The next version used a variable regulator with a max output of about 1050 PSI.


DragonSlayer said...

Ar tink/22 multi: No, you have me beat! My poor planes are mothballed! I too love RC. but must admit even though I purchaced a new 6 chnl. radio less than a year ago, (wife still askes me why), cause it is unused! In my defense I did taxi the Mrs. Martha around the yard! (Mrs. Martha is a local design) Comparible to the likes of Cap 21? Rated for a 40,w/ OS Max 60 it is an ANIMAL! Rate of climb is AWSOME! Low level fly bys are Impresive! Anyway,glad you got me thinking,Last 2 years Ive become so addicted to airguns, thats all I do! Maybe tom. I should see if I can still taxi, maybe some touch & go??LOL. Your friend,Tim.

DragonSlayer said...

Ar Tinkerer: Saw the new reveiw vidio by Paul Capella on 850 today. Nice gun! (I knew it was). I think he started w/ siver stings?,dont know about 22 but in 177 I cant hit ANYTHING with them. Then he shot Hobbys, From a bench I could shoot groups better than that w/ my G-1 ! I dont understand why he did not use a little more "mainstream" pels. for the 850. Im thinking CP brown box,JSB, Super domes,ect.? Dont get me wrong I LIKE HIS REPORTS! I feel short changed,I know 850 is better than that! W/850 & slow fire I would expect at 20 yrds. all/most shots to be in the "white" on a Gamo target. Ive wanted an 850 for some time now, but he is an expert,honestly those groups were not what I expected. I dont think you would have ever invested the time & effort you have on 850 if it did you like I saw today. What pels. do you shoot? P.C. if you read this dont be mad ! Give the 850 another go w/ other pels.! Hope all is well Multi.!! Tim.

A.R. Tinkerer said...


I read the review at where the accuracy is quite good with RWS Superdomes. I also figured I could adapt a 2260 barrel to the AirMagnum if I need to. So far I have been shooting JSB Exact Jumbos.

A.R. Tinkerer

A.R. Tinkerer said...

Sorry, that URL didn't all get in. The link is

Just in case this gets cut off (it looks like it might), the last part is:

A.R. Tinkerer

DB said...

RC Airplane guys. One of my ultimate dreams would be to mount a fully auto BB gun to an airplane and do strafing runs on scale fake air bases.

Of course the risk would be too great I'm sure but what fun that would be. Especially if you could mount a small camera on the plane.

Maybe an airsoft auto... safer anyway.

Please keep posting. I like hearing your great ideas that do work.

A.R. Tinkerer said...


Thanks, I plan on the next post sometime this week.


NiTr0_FiSh said...

.22 multi-shot,
This is cool! I'm looking forward to hearing what regulated 1500 psi nitrogen does.

I'm doing basically the same thing to my Crosman 2250. I have a 3000 psi tank & just got an Air American Raptor Rex regulator that will allow up to 1200 psi. I'll be trying nitrogen as soon as I get my Boss Max valve installed with more than the 1 stock screw. (Don't want to rip the valve away from the inside of my 2250).

I'm hoping 1200 psi might push this 2250 close to the 800 fps range. It chronys out now at 535 fps with CO2 & a heavy hammer spring using Crosman pointed premium pellets.

A.R. Tinkerer said...

Hey Nitr0_fish,

Thanks for the visit!

I don't know exactly where this project will end up, but it may end up with 1000PSI HPA tank and a custom valve. I've had some difficulties that I will blog soon.

I was originally going to do the same thing as you are doing to your 2250 only to my Crosman custom pistol. I drew out some sketches and the external tank looked clumsy so I threw out that idea.

My next idea was to use a 2260 tube to convert to bulk fill. However, now that the Discovery is out, I plan to use a Discovery valve, tube and fill adapter to convert to PCP (actually it could use CO2 like the Discovery too). It will require cutting and threading one end of the tube and drilling an extra hole, but I think it will probably fit otherwise. I'll have to keep the tube cool so it won't lose its heat treatment. We'll see how hard it is when I get the parts!

Let me know how your project goes!


Anonymous said...

dude, I do not think it`s a good idea to shoot any animals with that gun,it does`nt kill like a fire arm, only hurts the animals.I think you should stop using this method, or somebudy should report you.

Anonymous said...

LOL nonny mouse :P

UK airgun spec is 12fp MAX
You can kill bunnys out to 60 yds
at that power with a head shot.
Learn to aim and shut yer trap

AirGunGuy said...

Wow - your going above and beyond! I would love to be able to spend some time experimenting and pushing the envelope. Congrats and I look forward to more posts. This is great!